This invention relates to well pipe hangers and their seals, and more particularly to liner hangers and packoffs for use in subsea wells.
During the process of drilling an oil or gas well a plurality of casing strings, each comprising lengths of pipe joined together in end-to-end fashion, are installed concentrically in and cemented to the well bore to prevent undesired entry of fluids residing in the surrounding earth strata and, in many instances, to prevent cave-in of the well which can occur if, for example, it penetrates loose sand or other types of unconsolidated formations. Usually each casing string is supported at and extends downward from the wellhead, but there are occasions when it is desireable to install a special casing, called a liner, that extends downwardly from near or at the lower end of the previously installed next larger casing. The liner is supported or hung on that casing by a hanger, and the annulus between the liner and the casing is sealed with cement and/or an annular assembly called a packer or packoff.
Prior to the present invention one of the problems with liner hangers is that they do not offer the ability to open ports for circulating fluids past the hanger while cementing the liner in place, and then close those ports once the cementing operation is finished. If the liner hanger is run into the well with a packer once the packer is set there is either no way to circulate cement past the packer to assure a seal or with a retrievable packer, without first retrieving the packer the hanger and the packer which consumes substantial, costly rig time. If no packer is used, reliance must be solely on the cement to establish the required seal, and problems with effecting a satisfactory seal by cement alone are well known in the drilling industry.